From Behavior of Water on Hydrophobic Graphene Surfaces to Ultra-Confinement of Water in Carbon Nanotubes

Abstract

In recent years and with the achievement of nanotechnologies, the development of experiments based on carbon nanotubes has allowed to increase the ionic permeability and/or selectivity in nanodevices. However, this new technology opens the way to many questionable observations, to which theoretical work can answer using several approximations. One of them concerns the appearance of a negative charge on the carbon surface, when the latter is apparently neutral. Using first-principles density functional theory combined with molecular dynamics, we develop here several simulations on different systems in order to understand the reactivity of the carbon surface in low or ultra-high confinement. According to our calculations, there is high affinity of the carbon atom to the hydrogen ion in every situation, and to a lesser extent for the hydroxyl ion. The latter can only occur when the first hydrogen attack has been achieved. As a consequence, the functionalization of the carbon surface in the presence of an aqueous medium is activated by its protonation, then allowing the reactivity of the anion.

Physical Interactions Tune the Chemisorption of Polar Anions on Carbon Nanostructures

“…For comparable tube diameters, the binding energy follows the order: (M-zigzag) (SC-zigzag) (M-armchair). Note that our results for graphene ( eV and d SA = 1.52 Å) and our observation of a weaker adsorption inside CNT agree with previous DFT calculations. , However, our results demonstrate the coexistence of two adsorption states and that the binding energy strongly depends on both the curvature and chirality of the nanotube.…”

“…However, for metallic CNTs, the higher the chiral angle, the lower the adsorption energies. In contrast to previous works, , we show that the OH – adsorption at short distance results from a polar covalent bond whose strength is tuned by repulsive physical interactions of dipole–dipole type.…”

“…As mentioned above, when an anion is chemisorbed on the carbon surface, the C 0 atom protrudes due to the local rehybridization from sp 2 to sp 3 that takes place around the adsorption region (see Figure ). Such protrusion has already been observed in previous DFT studies of OH – adsorbed on graphene and SWCNTs . Indeed, the analysis of the carbon surface deformation can inform about the nature of the adsorption process. ,, The protrusion height h can be defined as the shortest distance between the C 0 atom and the plane made by its three adjacent C 1 atoms, that is, , where θ p (=θ σπ – 90°) denotes the pyramidalization angle and θ σπ is the average bond angle ⟨O–C 0 –C 1 ⟩ (see Figure a).…”

“…Such protrusion has already been observed in previous DFT studies of OH − adsorbed on graphene 15 and SWCNTs. 17 Indeed, the analysis of the carbon surface deformation can inform about the nature of the adsorption process. 9,29,32 The protrusion height h can be defined as the shortest distance between the C 0 atom and the plane made by its three adjacent C 1 atoms, that is h = a C 0 C 1 sin θ p , where θ p (=θ σπ − 90 o ) denotes the pyramidalization angle and θ σπ is the average bond angle ⟨O-C 0 -C 1 ⟩ 9 (see Fig.…”

Highly Effective Multifunctional Solar Evaporator with Scaffolding Structured Carbonized Wood and Biohydrogel

“…To study the interaction between water molecules and quasi-2D materials, the first-principles calculation was carried out using the Vienna ab initio simulation package (VASP). − Ti 3 C 2 (OH) 2 was used to stand for the MXene. A graphite monolayer with oxygen-containing groups was used as the model of the CW, and the oxygen-containing groups in it were determined based on the FT-IR result of the CW (Figures , S2, and S11).…”